Weak toFighting ×1.6

Attacker	Type	Moveset	DPS
Lucario	FightingSteel	Force PalmAura SphereLegacy	40.1
Pheromosa	BugFighting	Low KickFocus Blast	36.7
Terrakion	RockFighting	Double KickSacred SwordLegacy	36.5
Blaziken	FireFighting	CounterAura Sphere	36.2
Kartana	GrassSteel	Fury CutterSacred Sword	34.6
Conkeldurr	Fighting	Force PalmFocus Blast	33.4
Keldeo	WaterFighting	Low KickSacred Sword	33.1
Breloom	GrassFighting	Force PalmDynamic Punch	33.0
Urshifu	Fighting	CounterDynamic Punch	32.7
Eternatus	PoisonDragon	Poison JabDynamax CannonLegacy	32.5
Marshadow	FightingGhost	CounterClose Combat	32.0
Mewtwo	Psychic	CounterFocus BlastLegacy	31.9

Overcast boosts the Fighting attacks above. Partly cloudy boosts Castform.

Level 40, 15 attack IV, costed against Castform's own defense and typing, one per evolution family.

Castform's moveset, CP and shiny All counters Raid board

Questions people ask

What is Castform weak to in Pokémon GO?

Castform takes 1.6 times from Fighting.

What's the best counter to Castform?

Lucario with Force Palm and Aura Sphere, worth 40.1 damage per second against Castform's own defense. The full ranking is above.